U.S. patent application number 14/131545 was filed with the patent office on 2014-06-12 for method and device for testing a liquid.
The applicant listed for this patent is Fredrik Straat, Sebastian Zamani. Invention is credited to Fredrik Straat, Sebastian Zamani.
Application Number | 20140157879 14/131545 |
Document ID | / |
Family ID | 47506303 |
Filed Date | 2014-06-12 |
United States Patent
Application |
20140157879 |
Kind Code |
A1 |
Zamani; Sebastian ; et
al. |
June 12, 2014 |
METHOD AND DEVICE FOR TESTING A LIQUID
Abstract
A measuring device (2) for testing a liquid (4) used as reducing
agent in connection with exhaust cleaning for exhaust gases from a
combustion engine. A temperature sensor (6) measures the
temperature in the liquid. An acoustic velocity measuring unit (8)
measures the acoustic velocity in the liquid. The measured first
temperature T1 for the liquid and a first acoustic velocity v.sub.1
for the liquid at the temperature T1 are delivered to a calculation
unit (10). The temperature sensor determines a second temperature
T2 for the liquid and delivers a temperature signal (12) to the
calculation unit (10). That unit calculates the absolute value of a
temperature difference .DELTA.T between T1 and T2, i.e.
.DELTA.T=|T1-T2, and compares .DELTA.T with a predetermined
threshold value T.sub.TH. If .DELTA.T exceeds T.sub.TH, the
acoustic velocity measuring unit (8) determines a second acoustic
velocity v.sub.2 for the liquid at the temperature T2 to deliver an
acoustic velocity signal (14) to the calculation unit (10), which
compares v.sub.1 and v.sub.2 with reference values v.sub.ref1 and
v.sub.ref2 for a reference liquid at the respective temperatures T1
and T2. An approved indicating signal (18) is generated if the
measured values v.sub.1 and v.sub.2 are within approved velocity
ranges, but not approved if v.sub.1 and v.sub.2 are not within
those ranges.
Inventors: |
Zamani; Sebastian;
(Stockholm, SE) ; Straat; Fredrik; (Stockholm,
SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zamani; Sebastian
Straat; Fredrik |
Stockholm
Stockholm |
|
SE
SE |
|
|
Family ID: |
47506303 |
Appl. No.: |
14/131545 |
Filed: |
July 3, 2012 |
PCT Filed: |
July 3, 2012 |
PCT NO: |
PCT/SE2012/050765 |
371 Date: |
January 8, 2014 |
Current U.S.
Class: |
73/64.53 |
Current CPC
Class: |
G01N 2291/0217 20130101;
G01N 29/326 20130101; G01N 29/024 20130101 |
Class at
Publication: |
73/64.53 |
International
Class: |
G01N 29/024 20060101
G01N029/024 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 11, 2011 |
SE |
1150657-3 |
Claims
1. A method for testing a liquid used as a reducing agent in
connection with exhaust cleaning for exhaust gases from a
combustion engine, characterised in that the method comprises the
steps of a) determining a first temperature T1 for the liquid; b)
determining an acoustic velocity v.sub.1 for the liquid at the
first temperature T1; c) determining a second temperature T2 for
the liquid; d) calculating the absolute value of a temperature
difference .DELTA.T between T1 and T2, i.e. .DELTA.T=.sym.T1-T2; e)
comparing .DELTA.T with a predetermined threshold value T.sub.TH,
and if .DELTA.T exceeds T.sub.TH, f) determining a second acoustic
velocity v.sub.2 for the liquid at the temperature T2; g) comparing
v.sub.1 and v.sub.2 with respective first and second velocity
reference values v.sub.ref1 and v.sub.ref2 for a reference liquid
at the respective temperatures T1 and T2, and h) generating an
indicating signal on the basis of the results of the comparison,
wherein the indicating signal is to the effect that the liquid is
approved if the measured value v.sub.1 and v.sub.2 are within
approved velocity ranges for the reference values, but not approved
if v.sub.1 and v.sub.2 are not within said approved velocity
ranges.
2. The method according to claim 1, in which T.sub.TH is 1.degree.
C.
3. The method according to claim 1, further comprising warming the
liquid in a controlled way after steps a) and b).
4. The method according to any one of claim 1, further comprising
determining at least one further temperature value and comparing
the at least one further temperature value thus determined with the
previous temperature values determined, forming temperature
differences and, if these temperature differences exceed specific
threshold values, determining velocity values at the respective
temperatures which are compared with velocity reference values for
the reference liquid.
5. The method according to claim 1, wherein the reference liquid is
liquid urea.
6. A measuring device configured for testing a liquid used as a
reducing agent in connection with exhaust cleaning for exhaust
gases from a combustion engine, wherein the device comprises: a
temperature sensor configured for measuring the temperature in the
liquid and an acoustic velocity measuring unit configured for
measuring the acoustic velocity in the liquid; a calculation unit;
the temperature sensor is configured for determining a first
temperature T1 for the liquid and for delivering on the basis
thereof a first temperature signal to the calculation unit; the
acoustic velocity measuring unit is configured for determining a
first acoustic velocity v.sub.1 for the liquid at the first
temperature T1 and for delivering on the basis thereof a first
acoustic velocity signal to the calculation unit; the temperature
sensor is configured for determining a second temperature T2 for
the liquid and for delivering on the basis thereof a second
temperature signal to the calculation unit, the calculation unit is
configured for calculating an absolute value of a temperature
difference .DELTA.T between T1 and T2, i.e. .DELTA.T=|T1-T2, and
for comparing .DELTA.T with a predetermined threshold value
T.sub.TH; if .DELTA.T exceeds T.sub.TH, the calculation unit is
configured for delivering a control signal to the acoustic velocity
measuring unit to determine a second acoustic velocity v.sub.2 for
the liquid at the second temperature T2 and configured for
delivering on the basis thereof a second acoustic velocity signal
to the calculation unit, the calculation unit is configured for
comparing T1 and T2 with respective first and second velocity
reference values v.sub.ref1 and v.sub.ref2 for a reference liquid
at the respective temperatures T1 and T2, and for generating, on
the basis of the results of the comparison, an indicating signal to
the effect that the liquid is approved if the measured values
v.sub.1 and v.sub.2 are within approved velocity ranges for the
reference values, but not approved if the measured values v.sub.1
and v.sub.2 are not within said approved velocity ranges.
7. The measuring device according to claim 6, in which T.sub.TH is
1.degree. C.
8. The measuring device according to claim 6, further comprising a
warming device configured for warming the liquid in a controlled
way after v.sub.1 has been determined.
9. The measuring device according to claim 6, configured for
determining at least one further temperature value and for
comparing the at least one further value thus determined with the
previous values determined, forming temperature differences and, if
the temperature differences exceed specific threshold values,
determining velocity values at the respective temperatures which
are compared with corresponding velocity reference values for the
reference liquid.
10. The measuring device according to claim 6, wherein the
reference liquid is liquid urea.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for testing a
liquid used as reducing agent in connection with exhaust cleaning,
and a measuring device for implementing the method, according to
the preambles of the independent claims.
BACKGROUND TO THE INVENTION
[0002] A combustion engine burns a mixture of air and fuel in order
to generate driving torque. The combustion process generates
exhaust gases which are released from the engine to the atmosphere.
The exhaust gases comprise nitrogen oxides (NO.sub.X), carbon
dioxide (CO.sub.2), carbon monoxide (CO) and particles. NO.sub.X is
a composite term denoting exhaust gases which consist primarily of
nitrogen oxide (NO) and nitrogen dioxide (NO.sub.2). An exhaust
post-treatment system treats exhaust discharges in order to
decrease them before they are released to the atmosphere. In an
exemplified exhaust post-treatment system, a dosing system injects
a reducing agent into the exhaust gases upstream of a selective
catalytic reduction catalyst (SCR catalyst). The mixture of exhaust
gases and reducing agent reacts in the SCR catalyst and thereby
reduces the amounts of NO.sub.X discharged to the atmosphere.
[0003] An example of a reducing agent is liquid urea, commercially
available in the form of AdBlue.RTM.. This liquid is a non-toxic
urea solution in water and is used to chemically reduce discharges
of nitrogen oxides, particularly from diesel-powered heavy
vehicles. AdBlue.RTM. has a freezing point of -11.degree. C. and
the maximum temperature is about 60-70.degree. C.
[0004] The reducing agent reacts with NO.sub.X in the SCR catalyst
to effect the NO.sub.X reduction. More specifically, the reducing
agent is broken down and forms ammonia (NH.sub.3) which then reacts
with NO.sub.X to form water (H.sub.2O) and nitrogen gas
(N.sub.2).
[0005] To achieve the NO.sub.X reduction described, NH.sub.3 has to
be stored in the SCR catalyst. For the SCR catalyst to work
effectively, this storage has to be at an appropriate level. In
more detail, the NO.sub.X reduction, the conversion effectiveness,
depends on the storage level. Maintaining high conversion
effectiveness in different operating states depends on maintaining
the store of NH.sub.3. The NH.sub.3 level does however have to be
lowered progressively as the temperature of the SCR catalyst rises,
to avoid NH.sub.3 discharges (i.e. surplus NH.sub.3 being released
from the SCR catalyst) which might decrease the conversion
effectiveness of the catalyst.
[0006] In brief, to meet stricter environmental requirements,
vehicle manufacturers are increasingly using SCR catalyst systems
to remove nitrogen oxides (NO.sub.X) from exhaust gases. This is
done by injecting ammonia solution into a SCR catalyst to help to
convert NO.sub.X particles to nitrogen gas and water. The exhaust
cleaning strategy needs to cater for sufficient NO.sub.X to be
converted while at the same time trying not to inject too much
reducing agent, for both environmental and operational economy
reasons.
[0007] Within the EU there are for example requirements concerning
exhaust emission levels and types of reducing agent to be used.
Future requirements may inter alia include it being possible to
determine the quality of the reducing agent used.
[0008] A way of determining reducing agent quality is to measure
the acoustic velocity in combination with measuring the
temperature.
[0009] The acoustic velocity in liquids may be determined by the
formula
v.sub.liquid= K(p)/.rho.(T))
in which K(p) is the liquid's compression factor, which depends on
the pressure p, and .rho.(T) is the density of the liquid.
[0010] As the density of liquids is temperature-dependent, this has
to be compensated for by measuring the temperature of the liquid.
In the same way, the liquid's compression factor is
pressure-dependent but to only a very small extent (relative to
atmospheric pressure).
[0011] FIG. 1 is a graph illustrating schematically the
relationship between acoustic velocity (m/s) and temperature for
the following liquids:
[0012] A: Glycol
[0013] B: Urea of AdBlue type
[0014] C: Diluted AdBlue
[0015] D: Water
[0016] The graph is to the effect that different liquids have
different acoustic velocities at different temperatures, but there
are liquids which have the same acoustic velocity at the same
temperature, e.g. glycol and brine, which have at about 35.degree.
C. the same acoustic velocity as AdBlue. Distinguishing between
these liquids involves using in addition, according to a known
device, a conductivity sensor and determining the conductivity of
the liquids. The fact that the conductivity of AdBlue differs from
that of glycol makes it possible to distinguish these liquids.
However, the involvement of a further sensor causes increased
complexity and consequently more expense and greater risk of error.
Moreover, the conductivity of AdBlue from different manufacturers
may differ substantially, likewise causing more risk of error.
[0017] Conducting measurements on a urea solution with an acoustic
sensor is described in a number of patent specifications discussed
briefly below.
[0018] US-2008/0280371 refers to an acoustic sensor adapted to
measuring the concentration of urea. The fact that changes in the
molecular weight of urea affect the acoustic velocity can be used
to determine the concentration. The acoustic sensor may be combined
with an NH3-sensitive sensor used to make sure that what is
concerned is urea.
[0019] DE-102006013263 refers to a method for determining the
concentration of urea solutions in a liquid on the basis of the
acoustic velocity in the liquid, which is determined by ultrasonic
sensors.
[0020] The specifications cited refer to devices for determining
urea quality but make no comparisons with other liquids.
[0021] The object of the present invention is to propose a method
and device which can provide assurance that the reducing agent is
approved and can do so in a way which does not increase the
complexity of the measurements and therefore does not increase
costs and the risks of error.
SUMMARY OF THE INVENTION
[0022] The above objects are achieved with the invention defined by
the independent claims.
[0023] Preferred embodiments are defined by the dependent
claims.
[0024] According to the invention, the acoustic velocity is
evaluated over a certain time, which means that the quality
measurement can be made more accurate and that it is then possible
with greater certainty to determine what type of liquid is in the
tank intended for reducing agent. This can be accomplished without
any conductivity measurements at all.
[0025] The present invention is based on the fact that acoustic
velocities differ at different temperatures. A vehicle's various
operating conditions cause the temperature of the liquid contained
in the tank intended for reducing agent to vary over time, e.g.
T.sub.night, T.sub.winter, T.sub.running, T.sub.stop,
T.sub.rest.
[0026] Determining the acoustic velocity for the liquid contained
in the tank intended for reducing agent at at least two different
temperatures and comparing these measured velocities with reference
values for the velocity for a reference liquid, i.e. an approved
liquid, makes it possible to obtain information about the degree of
correspondence between the liquid and the reference liquid, and if
the liquid in the tank corresponds sufficiently, i.e. is within a
given range, the conclusion is that it is an approved liquid.
[0027] It happens in certain cases that the liquid in the tank
intended for reducing agent does not reach the temperature required
for making the desired quality measurements/distinction. The
present invention then makes it possible to use the heating system
provided for thawing the liquid in hoses and in the tank to raise
the temperature. The electrically heated hoses and water valves
which help to circulate the engine cooling water in the tank
containing the liquid are controlled by a control unit on board the
vehicle which also communicates with the calculation unit in the
measuring device.
[0028] The invention affords inter alia the advantage of making it
possible to distinguish two or more different liquids without using
a conductivity sensor.
[0029] A further preferred embodiment makes it possible to use an
atmospheric pressure sensor to calculate the liquid's compression
factor and thereby further increase the measurement accuracy.
BRIEF DESCRIPTION OF DRAWINGS
[0030] FIG. 1 is a graph schematically illustrating the
relationship between acoustic velocity and temperature for
different liquids.
[0031] FIG. 2 is a schematic block diagram illustrating the present
invention.
[0032] FIG. 3 is a flowchart illustrating the method according to
the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0033] The invention will now be described with reference to the
block diagram in FIG. 2. The invention comprises a measuring device
2 adapted to testing a liquid 4 used as reducing agent in
connection with exhaust cleaning for exhaust gases from a
combustion engine (not depicted). The engine is preferably on board
a vehicle, e.g. a truck or bus, but other applications are also
possible, e.g. on watercraft or in the engineering industry. The
reducing agent is for example a urea solution, e.g. of the AdBlue
type.
[0034] The measuring device 2 comprises a temperature sensor 6
adapted to measuring the temperature in the liquid 4 and an
acoustic velocity measuring unit 8 adapted to measuring the
acoustic velocity in the liquid. A level gauge (not depicted) is
often also provided to measure the level of the liquid 4 in the
tank intended for reducing agent.
[0035] The acoustic velocity measuring unit 8 may be a conventional
acoustic measuring device comprising a transmitter which emits an
acoustic wave into the liquid 4, and a receiver which detects the
reflected sound wave. Other acoustic measuring devices may also be
used within the scope of the present invention.
[0036] The size of the tank intended for reducing agent is known,
which makes it easy to calculate the acoustic velocity by measuring
the time between the wave being emitted and the reflected sound
wave being detected and calculating the velocity by dividing the
distance by the measured time.
[0037] The measuring device 2 further comprises a calculation unit
10.
[0038] The temperature sensor 6 is adapted to determining a first
temperature T1 for the liquid 4 and to delivering on the basis
thereof a temperature signal 12 to the calculation unit 10. The
acoustic velocity measuring unit 8 is also adapted to determining a
first acoustic velocity v.sub.1 for the liquid 4 at a temperature
T1 and to delivering on the basis of a measured velocity an
acoustic velocity signal 14 to the calculation unit 10. The
temperature sensor 6 is adapted to determining a second temperature
T2 for the liquid 4 and to delivering on the basis thereof a
temperature signal 12 to the calculation unit. The calculation unit
10 is adapted to calculating the absolute value of a temperature
difference .DELTA.T between T1 and T2, i.e. .DELTA.T=|T1-T2|, and
to comparing .DELTA.T with a predetermined threshold value
T.sub.TH. If .DELTA.T exceeds T.sub.TH, a control signal 16 is
delivered to the acoustic velocity measuring unit 8 to determine a
second acoustic velocity v.sub.2 for the liquid 4 at the
temperature T2 and to deliver on the basis of the measured velocity
an acoustic velocity signal 14 to the calculation unit 10.
[0039] According to an embodiment, T.sub.TH is 2.degree. C. but any
suitable value larger than 1.degree. C. may be chosen.
[0040] In other words, the measurement of the second acoustic
velocity v.sub.2 should take place when the temperature difference
exceeds the threshold value T.sub.TH.
[0041] The temperature measurement may for example be done
continuously at a predetermined measuring interval, e.g. of the
order of one or a few seconds or minutes, and the velocity
measurement is only done when the temperature difference is large
enough.
[0042] The calculation unit 10 is then adapted to comparing v.sub.1
and v.sub.2 with respective first and second velocity reference
values v.sub.ref1 and v.sub.ref2 for a reference liquid at the
respective temperatures T1 and T2 and to generating on the basis of
the result of the comparison an indicating signal 18. The reference
liquid is for example a urea solution which meets all the quality
requirements.
[0043] The indicating signal 18 is to the effect that the liquid 4
is approved if the measured values v.sub.1 and v.sub.2 are within
approved velocity ranges for the reference values, in which case
the indicating signal contains for example the information "OK",
and that the liquid 4 is not approved if the values v.sub.1 and
v.sub.2 are not within said approved velocity ranges, in which case
the indicating signal contains for example the information "not
OK".
[0044] The approved velocity ranges may for example be chosen as a
maximum percentage deviation from the velocity reference values.
This deviation may be of the order of one or a few percent, e.g.
maximum 5%.
[0045] As discussed above, the liquid 4 in the tank intended for
reducing agent will be at different temperatures depending on the
different operating situations which the vehicle may be in. Inter
alia it may however be desirable to conduct the measurement even
when the liquid 4 has undergone no temperature change due to the
vehicle's operating situation.
[0046] The device then comprises, according to an embodiment, a
warming device 20 adapted to warming the liquid 4 in a controlled
way after v.sub.1 has been determined. For example, the warming
device 20 may take the form of the heating system provided to thaw
the reducing agent in hoses and in the container. The warming
device may be controlled by a control signal 22 generated by the
calculation unit 10.
[0047] It is of course possible within the scope of the invention
to determine at least one further temperature value and in that
case to compare the further value or values thus determined with
the previous values determined, to form temperature differences
and, if these exceed specific threshold values, to determine
velocity values at the respective temperature or temperatures which
are compared with corresponding velocity reference values for the
reference liquid. This would further increase the reliability of
the measurements.
[0048] The method will now be described in detail with reference to
FIG. 3, which is a flowchart illustrating the method according to
the invention.
[0049] The invention relates also to a method for testing a liquid
used as reducing agent in connection with exhaust cleaning for
exhaust gases from a combustion engine.
[0050] The method comprises the steps of:
[0051] a) determining a first temperature T1 for the liquid;
[0052] b) determining an acoustic velocity v.sub.1 for the liquid
at the first temperature T1;
[0053] c) determining a second temperature T2 for the liquid;
[0054] d) calculating the absolute value of a temperature
difference .DELTA.T between T1 and T2, i.e. .DELTA.T=|T1-T2|;
[0055] e) comparing .DELTA.T with a predetermined threshold value
T.sub.TH which is preferably 2.degree. C. but may also be any
suitable value greater than 1.degree. C.
[0056] If .DELTA.T exceeds T.sub.TH, the following steps are
performed:
[0057] f) determining a second acoustic velocity v.sub.2 for the
liquid at the temperature T2;
[0058] g) comparing v.sub.1 and v.sub.2 with respective first and
second velocity reference values v.sub.ref1 and v.sub.ref2 for a
reference liquid at the respective temperatures T1 and T2, and
[0059] h) generating an indicating signal on the basis of the
results of the comparison.
[0060] The indicating signal is to the effect that the liquid is
approved if the measured values v.sub.1 and v.sub.2 are within
approved velocity ranges for the reference values, but not approved
if v.sub.1 and v.sub.2 are not within said approved velocity
ranges.
[0061] The approved reference liquid is for example liquid urea
which meets all the quality requirements.
[0062] As discussed above, it may in certain contexts be
appropriate instead to actively warm the liquid in a controlled
way, which may be done between steps b) and c).
[0063] It is also possible to make further temperature measurements
by determining at least one further temperature value and comparing
the further value or values thus determined with the previous
values determined, forming temperature differences and, if these
exceed specific threshold values, determining velocity values at
the respective temperature or temperatures which are compared with
velocity reference values for the reference liquid. The result is a
still more reliable measurement result.
[0064] The present invention is not restricted to the preferred
embodiments described above. Sundry alternatives, modifications and
equivalents may be used. The above embodiments are therefore not to
be regarded at limiting the invention's protective scope which is
defined by the attached claims.
* * * * *